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* A boy, 14, being transferred to an adult prison wearing a "spit hood", a sack like mask fitting over the head (2014)

* A guard saying "I'll pulverise the f***er" as a youth in isolation bangs at the windows (2014).

THE FEDERAL GOVERNMENT RESPONSE:

* Prime Minister Malcolm Turnbull announced a royal commission.

"We want to know how this came about, we want to know what lessons can be learned from it, we want to know why there were inquiries into this centre which did not turn up the evidence and the information that we saw on Four Corners last night."

"I have full confidence in the majority of custodial officers working in the Northern Territory's institutions. They have a challenging and difficult job, one that not many people wish to do. To those officers I want to say, you have my full support for the work that you do in upholding our laws."

EARLIER INVESTIGATIONS:

* A 2015 independent review commissioned by the NT government found no evidence of a "systemic culture of unreasonable use of force" except in some isolated cases.

* NT Children's Commissioner Howard Bath in 2012 investigated the prolonged mistreatment of one boy. The report was never made public.